Plasma fired steam generator system

ABSTRACT

A system for generating high pressure steam from dirty water uses a combination of submerged plasma arcs and electrical resistive heating. Dirty water from steam assisted gravity drainage, or other dirty water producing process, which needs to be converted into high pressure steam, is fed directly without any pre-treatment, into a plasma fired steam generator, powered by submerged electrodes. The combination of electric arc plasma and resistive heating is created between the submerged electrodes. The heat so generated will boil the water portion of the dirty water feed to generate steam that is collected in a steam space and then removed therefrom. The solids and other residues (residual sludge) present in the feed water settle down at the bottom of the steam generator and are removed via a blow-down stream. The plasma arcs are used to intermittently remove any scaling or solid deposits that can accumulate on the electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority on U.S. Provisional Application No.61/877,150, now pending, filed on Sep. 12, 2013, which is hereinincorporated by reference.

FIELD

The subject matter of the present disclosure relates to steamgeneration.

BACKGROUND

Bitumen contained in ore bodies (oil sands) is recovered using eithersurface mining with subsequent physical/mechanical recovery unitoperations or with an in situ recovery process referred to as Steamassisted gravity drainage (SAGD). About 80-85% of the total oil sandsreserves employ the SAGD process. In the SAGD process, steam generatedat a centralized boiler house using once through steam generators (OTSG)is transported to oil wells located at distances anywhere between 2 and10 km. The steam pressure at the OTSG is 10 MPa, while at the inlet ofthe well it is 4 MPa and inside the well it is 2.5 MPa. The water-oilemulsion recovered from the oil well is then pumped to the centralprocessing facility. Oil and water are separated from this emulsionusing knock-out drums. Since environmental regulations require a highrecycle ratio of water, the dirty water is re-used using a series ofwater cleaning unit operations before it can be used as boiler feedwater for the OTSGs.

The existing water recovery/steam generation process has drawbacks andlimitations that include, but are not limited to, high capital costs,long installation and commissioning times, long start-up and shutdowntimes and low process availability. The current process is also noteconomically viable for smaller or isolated well pads.

SUMMARY

It would thus be highly desirable to be provided with a system or methodthat would at least partially address the disadvantages of the existingtechnologies.

The embodiments described herein provide in one aspect a steamgenerating system, which uses a combination of submerged plasma arcs andresistive heating, to generate high pressure steam from dirty feedwater.

The embodiments described herein provide in another aspect a plasmafired steam generator, which uses either a single set of electrodes ormultiple sets of electrodes to generate high pressure steam from thefeed water.

The embodiments described herein provide in another aspect an electrodeseal system which can provide the seal between the electricallyconducting electrodes and the body of the plasma fired steam generator.

The embodiments described herein provide in another aspect an endlessscrew mechanism, which can provide great precision, used to control therelative position of the electrically conducting electrodes and thusindependently control the current for each AC phase and the power inputto a plasma fired steam generator (PFSG).

The embodiments described herein provide in another aspect a plasmafired steam generator, comprising either a single set of electrodes ormultiple sets of electrodes to generate high pressure steam from feedwater.

The embodiments described herein provide in another aspect an electrodeseal system for use between electrically conducting electrodes and abody of a plasma fired steam generator.

The embodiments described herein provide in another aspect an endlessscrew mechanism for use in controlling a relative position ofelectrically conducting electrodes and thus independently controlling acurrent for each AC phase and a power input to a plasma fired steamgenerator.

The embodiments described herein provide in another aspect a steamgenerating system, comprising a combination of at least one submergedplasma arc and resistive heating, adapted to generate high pressuresteam from dirty feed water.

The embodiments described herein provide in another aspect a method forgenerating steam, comprising: providing a steam generator; feeding dirtywater to the steam generator; and submitting the dirty water to at leastone submerged plasma arc and to resistive heating, such as to generatehigh pressure steam.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the embodiments described herein and toshow more clearly how they may be carried into effect, reference willnow be made, by way of example only, to the accompanying drawings whichshow at least one exemplary embodiment, and in which:

FIG. 1 shows a schematic representation of a plasma fired steamgenerator (PFSG) system according to one of various exemplaryembodiments;

FIGS. 2a and 2b show schematic representations of the PFSG with a singleset of electrodes and with multiple sets of electrodes, respectively;

FIG. 3 shows a schematic representation of electrode seals, which areused to seal a gap between a current carrying electrode and a body ofthe PFSG; and

FIG. 4 shows a schematic representation of an electrode motion system.

DESCRIPTION OF VARIOUS EMBODIMENTS

The present system uses a combination of plasma arcs and resistiveheating, generated either using alternating current or direct currentand submerged under water, to produce steam from untreated (dirty)water. The energy needed to produce steam is provided by the plasma arcsstruck between electrically conducting electrodes, as well as thewater's electrical resistivity. A high current, low voltage powersource, either AC or DC, is used to generate and power the plasma arcs.

In the present system, called the plasma fired steam generator (PFSG)process, the dirty water coming, for example, from the free water knockouts (FWKO) is directly injected into a plasma fired steam generator.The plasma arcs submerged in the water, along with resistive heating,deliver the necessary energy to evaporate water and produce highpressure steam in a continuous manner.

The PFSG functions in a similar way to an electric arc furnaceprocessing scrap steel, but using steel electrodes instead of graphiteelectrodes, and immersed in water, instead of in a mass of steel scrap.The intense heat of the plasma will vaporize water at a high rate. Themain advantage of using plasma over gas or electric heating elements isthat the intense heat of the plasma allows the electrodes tips to remainclean, despite the precipitation of solids caused by the evaporation ofdirty water. This allows for a high throughput of steam production witha small installation footprint.

For the SAGD applications, the Plasma Fired Steam Generator (PFSG) canbe used to produce high pressure (4 MPa) steam from “dirty” waterdirectly at the well pad. This eliminates the costly and sometimesdangerous transportation of high pressure steam over long distances,allows for quick expansion and allows for the use of brackish water as amake-up water source when required.

Furthermore, the PFSG can be built in modular sections, allowing forinstallation at a single well, or for an entire well pad, as required.

As shown in FIG. 1, the dirty water used to produce steam is fed, via afeed inlet 8, to a plasma fired steam generator (PFSG) 1, powered bysubmerged electrodes 2. The water portion of the feed is evaporated toform steam, whereas the solid portion settles at the bottom of the steamgenerator 1. The steam generated is removed via a steam outlet 10 fromthe steam space, and the residual sludge is removed as a blowdown streamvia a residue outlet 12. The plasma arcs are used to intermittentlyremove any scaling or solid deposits that can accumulate on theelectrodes. A vessel of the PFSG 1 is generally denoted by reference 14.

Therefore, dirty water from the Steam Assisted Gravity Drainage (SAGD),or other dirty water producing process, which needs to be converted intohigh pressure steam, is fed typically directly without any pretreatmentinto the plasma fired steam generator (PFSG) 1. A combination ofelectric arc plasma and resistive heating is created between thesubmerged electrodes 2. The heat so generated will boil the water togenerate steam which is collected in the steam space. The solids andother residues present in the feed water settle down at the bottom ofthe (PFSG) 1, and are removed via a blowdown stream.

FIGS. 2a and 2b show the electrode arrangement for the PFSG 1 with asingle set of electrodes and multiple sets of electrodes, respectively.To achieve higher steam throughput, PFSGs 1 equipped with multiple setsof electrodes are used, whereas smaller throughput steam generators 1use only a single set of electrodes.

In the 3 phase AC arrangement with a single set of electrodesillustrated in FIG. 2a , the PFSG includes a vertical steel cylindricalvessel 14 a with spherical ends designed to meet the appropriaterequirements for steam pressure vessels. The three alternating current(AC) electrodes are located, for instance, midway up the reactor'ssidewall and are positioned at 120 degrees from each other. A steamoutlet 10 a is located, for instance, at the top of the reactor.

In the multiple set of electrodes 3 phase AC arrangement of FIG. 2b ,the reactor includes a horizontal steel cylinder 14 b with sphericalends, which meets the appropriate requirements for steam pressurevessels. The AC electrodes are Installed, for example, as 6 trios (theelectrodes of each trio being positioned at 120 degrees from one anotherabout the reactor's circumference), for a total of 18 electrodes. Asteam outlet 10 b is located, for instance, in the middle of thereactor, with three sets of electrodes on each side. For larger capacityPFSGs 1, additional sets of electrodes would be provided. For smallercapacity PFSGs 1, between 2 and 6 sets of electrodes would be used.

An electrically insulating, high pressure seal mechanism is used to seala gap between the current carrying electrodes 2 and a body of the PFSG1, as shown in FIG. 3. To maintain electrical insulation and thus avoida flow of electric current through the body of the PFSG 1, electricallyinsulating plates 3 and sleeves 4 are used.

In the AC mode of operation, the power input to the PFSG 1 is controlledby varying the power supply voltage set-point and also by varying therelative position of the electrodes with each other. Varying theposition of the electrodes relative to each other allows for controllingthe current, and consequently the total power input.

In the DC mode of operation, the power input to the PFSG 1 is controlledby varying the power supply current set-point and also by varying therelative position of the electrodes with each other. Varying theposition of the electrodes relative to each other allows for controllingthe voltage, and consequently the total power input.

The electrodes of the PFSG 1 are moved using an electrode motion system,for example an endless screw mechanism 5, as shown in FIG. 4, which canbe controlled with great precision and can maintain the electrodepositions against the force of the high pressure steam. Electrode damps6 are fabricated from electrically conductive materials and, as theyclamp onto the electrodes, they provide the necessary contact for theflow of electric current.

Although the application mentioned hereinabove of the present PlasmaFired Steam Generator (PFSG) 1 is for the extraction of bitumen from theoil sands, it is however noted that the PFSG can be used in anyIndustrial processes where a source of dirty water must be purifiedbefore conversion to steam at low or high pressure.

Finally, while the above description provides examples of theembodiments, it will be appreciated that some features and/or functionsof the described embodiments are susceptible to modification withoutdeparting from the spirit and principles of operation of the describedembodiments. Accordingly, what has been described above has beenIntended to be illustrative of the embodiments and non-limiting, and itwill be understood by persons skilled in the art that other variants andmodifications may be made without departing from the scope of theembodiments as defined in the claims appended hereto.

1.-7. (canceled)
 8. An endless screw mechanism for use in controlling arelative position of electrically conducting electrodes and thusindependently controlling a current for each AC phase and a power Inputto a plasma fired steam generator.
 9. A steam generating system,comprising a combination of at least one submerged plasma are andresistive heating, adapted to generate high pressure steam from dirtyfeed water.
 10. The steam generating system of claim 9, comprising avessel, at least one inlet to the vessel for feeding the dirty feedwater therein, and at least one first outlet for removing the highpressure steam from the vessel.
 11. The steam generating system of claim9, comprising at least one second outlet for removing solids and otherresidues from the vessel.
 12. The steam generating system of claim 9,wherein there are provided a plurality of submerged plasma arcs.
 13. Thesteam generating system of claim 9, comprising either a single set ofelectrodes or multiple sets of electrodes to generate the high pressuresteam from the dirty feed water.
 14. The steam generating system ofclaim 9, wherein there is provided an electrode seal system betweenelectrically conducting electrodes and a body of the vessel.
 15. Thesteam generating system of claim 14, wherein electrically insulatingplate(s) and sleeve(s) are provided to maintain electrical Insulationand thus avoid a flow of electric current through the body of thevessel.
 16. (canceled)
 17. The steam generating system of claim 9,wherein the steam generating system Includes a plasma fired steamgenerator.
 18. A method for generating steam, comprising: providing asteam generator; feeding dirty water to the steam generator; andsubmitting the dirty water to at least one submerged plasma arc and toresistive heating, such as to generate high pressure steam.
 19. Themethod of claim 18, further comprising the step of removing the highpressure steam from the steam generator.
 20. The method of claim 18,further comprising the step of removing a residual sludge from the steamgenerator.
 21. The method of claim 18, wherein the dirty water isobtained from steam assisted gravity drainage, or another dirty waterproducing process.
 22. The method of claim 18, wherein the dirty wateris fed directly without any pre-treatment into the steam generator. 23.The method of claim 18, wherein there are provided a plurality ofsubmerged electrodes.
 24. The method of claim 18, wherein a combinationof electric arc plasma and resistive heating is created betweensubmerged electrodes.
 25. The method of claim 18, wherein the heatgenerated is adapted to boll a water portion of the dirty water togenerate the high pressure steam.
 26. The method of claim 18, whereinthe high pressure steam is collected in a steam space and is thenremoved therefrom.
 27. The method of claim 18, wherein solids and otherresidues (residual sludge) present in the dirty water settle down at abottom of the steam generator and are removed via a blow-down stream.28. The method of claim 18, wherein the plasma arcs are used tointermittently remove scaling or solid deposits that may haveaccumulated on the electrodes.